Cast iron alloy and method of producing the same



June 7, 19.38.. w. J. sPARLlNG CAST IRON ALLOY AND METHOD OF PRODUCING 'THE SAME 3 Sheets-Sheet 1 Filed June 2l, '41935 asn/neo ala/wurm? li/Ey. 5l

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June 7, 1938.

W. J. SPARLING CAST IRON ALLOY AND METHOD OI PRODUCING THE SAM 3 sheets-sheet 2 Filed June 2l, 1935 HOU/P6 W. J. SPARLING CAST IRON ALLOY AND METHOD OF PRODUCING THE SAM June 7, 1938. v

Filed June 21. 1935 3 Sheets-Sheet 3 FERRITE m m m G SPHEROIDIZED :m NTITE SUBSTAN- TIALLY UNIFoRMLY DISTRIBUTED THROUGHQUT THE: MA1-nn:

FEHRITEi GRAIN ARIES l FERRITE MENTRE WHICH HAS No'r MIGRATED m I m m H P S SP EROIDIZED CEMENTITE WHICH HAS mm mm um mmm Mmm mwa. MLG

Patented June 7, 1938 y PATENT OFFICE cAs'r IRON ALLOY AND METHOD OF PRO- DUOING THE SAME William J. Sparling, Milwaukee, Wis., assigner to Chain Belt Company, Milwaukee, Wis., a corporation of Wisconsin Application June 21, 1935, Serial No. 27,766 7 claims. (o1. 14s-21.8) g

This invention relates to ferrous metal alloys, and more especially to ferrous alloys which include graphitizing accelerating and retarding elements; for example, alloys of iron, carbon, copper and manganese. The invention also comprises a novel heat treatment of castings made from such ferrous metal alloys; and one of its principal Objects is to produce a. white iron alloy suitable for making white iron castings, which, after being subjected to said heat treatment, will possess higher ductility, higher impact value, higher tensile strength, higher resistance to corrosion, and higher resistance to Ween-than .have been heretofore obtainable in white iron castings, thereby greatly increasing the durability of such castings in practically every use tol which cast iron products are put.

A further object is the improvement of ferrous metal alloys, and more especially ferrous alloys having inclusions of carbon and graphitizing accelerating and retarding elements, for example alloys of iron, carbon, copper, and manganese. The invention has for a further object'.

- a novel heat treatment of castings made from,

Such ferrous metal alloys; and its main object is to produce a white iron alloy suitable for mak-- ing white iron castings, which-after being subjected tothe novel heat treatment described herein will possess higher ductility, higher resistance to impact forces, a greater tensile strength,

higher resistance to corrosion, and higher frictional w r resistance, than have, so far as heretoore known, been obtainablein castings made of white iron; and thereby greatly increasing many of the d esrable qualities of such castings.

The said ferrous metal alloys and the heat treatment herein described are inter-related to the extent that if the said alloys are subjected to the said heat treatment, the better results stated above are obtained to a greater degree than if other known heat treatments are employed.

The-ferrous metal alloys and the heat treatment of this invention are so inter-related that the desirable qualities heretofore mentioned are attained to a higher degree in castings made of the alloy and heat treated according to the method of this invention, than are secured incastings of the alloy heat treated in a different manner, or in castings of a diierent composition when heat treated in accordance with .the method of this invention.

elements are so proportioned as to impart to the cast metal, when fractured, a silver-white appearance. TheA usual White cast iron of commerce also contains some sulphur, phosphorus, and manganese, all in small quantities, and the iron mayvalso contain traces of other elements as impurities which do not have an appreciable effect upon the physical properties of the cast product.

The amounts of carbon and silicon, and their arrangement in the cast metal, are such as to distinguish the iron from steel as generally dened, and are so proportioned as to prevent the separationof the carbon into ake graphite during the cooling or freezing of the cast metal, thereby distinguishing white cast iron from gray castiron.' While such metal as cast is not ductile but very hard and brittle, it may be subjected to a heat-treatment, commonly termed malleableizing, to develop therein appreciable ductility.

White cast iron for the malleableizing treatment, as heretofore usually made, has a composition approximately Within the following limits- Per cent Carbon 1.90 to 3.00 Silicon 1.30 to 0.60 Phosphorus 0.08 to 0.16 Sulphur 0.05 to 0.12 -Manganese- 0.20 to 0.40

Tensile strength pounds per sq. in 45,000 to 60,000

ElasticA limit do 32,000 to 38,000 Elongation in 2" per cent 25 to 10 Hardness (Brinell) 115 toV 140 Impact value foot pounds to '7 The impact values as herein stated are the average values obtained in numerous tests conducted with a specially constructed impact machine which is similar to the standard Charpy machine, with the exception that my new machine is designed to take rough cast testbars 1%" sq. by 3 long, while the standard Charpy machine is designed to take machine-finished test bars of smaller size. In my work the test bars were not notched; as required in the standard Charpy test, because notching the surface of a malleable casting, or a casting made of my special alloy, more appreciably decreases the impact value than would be occasioned on a steel test bar usually" used in the Charpy method of determining impact value. However, the specic figures herein shown for impact in foot pounds are representative of the impact value and are comparable to standard Charpy values but not to the same scale because of the size and section of the specimens. The gures for impact are comparable between themselves and give a good indication of the impact value of malleable iron and my alloyed ferrous metal.

The average corrosion resistance of ordinary malleable iron of the above physical properties,

as I have determined it, is given in the following table and the figures stated are the average of a great number of tests conducted by me, and show the rate of loss of metal in milligrams per square centimeter of exposed surface of samples during a uniform xed time period of immersion in the following solutions.

10% salt water solution 0.052 5% sulphuric acid solution 23.352 25% tannic acid solution 0.087 5% lactic acid solution 1.190 5% hydrochloric acid solution 16.107

The malleableizing of white cast iron may be briefly stated as separating by heat-treatment the chemically combined iron and carbon (Fesc) into iron (ferrite) and finely divided nodules of temper carbon or graphite. To secure the better results of the process, it is essential that substantially all of the carbon be combined chemically with the iron when cast,that is, there should be no free graphtic carbon in the cast metal before practicing the malleableizing process. Another essential is that the silicon, which acts as a graphitizer, be within-well defined lim.

its, as is known to those acquainted with the art. It is well known that certain lelements, when combined .with iron containing carbon, act as retarders, that is, impede graphitization of the carbon; and that others act as accelerators, that is, promote graphitization, during the malleableizing process. For example, sulphur, manganese and chromium are retarders, while aluminum, nickel, and copper, in small quantities, are accelerators ofthe phenomena of graphitization. Retarding elements are characterized as forming compounds with molten iron which may be said to act as lms that apparently prevent the carbon molecules from migrating together during the ma-lleableizing process, which film formations however, are preventable by appropriate changes in composition of the metal charge before melting. For example, it is well known that sulphur in white iron forms sulphur-iron compounds, apparently having a filming character which prevents graphitization. On the other hand, it is also well known, that sulphur will combine with any manganese in the molten metal in preference to iron, forming small -rounded nodules of manganese sulphide which apparently do not interfere with the graphitization process, and therefore it is common practice to have suihcient manganese in the metal to insure the sulphur combining therewith. w

The art has heretofore sought a manganese value slightly in excess of twicethe sulphur content to act as a neutralizen but not in an amount greater than 0.6%, as larger percentages of manganese 'have tended to make the iron dinivcult to malleableize, and after the malleableizing process the metal is apt to be quite hard and deficient in ductility.

Heretofore, in adding copper to iron, it has been customary to also introduce chromium to neutralize the so-called softening effect (which for example may be due to graphitizing under certain temperatures) of copper on the product. I have discovered that with an excess of manganese over the normal amount of less than .60%, copper may be introduced into the molten metal in quantities as great as 1.5 percent without adverse effect, and with the use of an excess of manganese, it is not necessary to have chromium in the mixture, as apparently the excess 0f manganese neutralizes any softening effect (which for example may be due to graphitizing under certain temperatures) the copper may have.

'I'he present invention is a development growing out of the broad invention described and claimed in the co-pendihg application of Maurice G. Jewett and Samuel C. Harris, Serial No. 564,634, led September 23, 1931, now Patent 2,008,452, dated July 16, 1935, in that it relates to a heat treated cast iron product in which the major portion of the carbon is in graphitic form, and the cementite is in spheroidized or globular form.

In the present invention, however, by alloying white iron with manganese in an amount above normal practice, and with copper above that heretofore proposed, I am enabled to secure a cast iron product in which, after heat treatment, the spheroidized cementite, instead of being substantially uniformly dispersed throughout the matrix, as in said prior invention, is re-arranged to apparently interlock at the grain-crystal boundaries of the ferrite and thereby make these cleavage planes stronger. It is this re-arrangement of the spheroidized cementite into interlocking relation, with criss-crossing of the ferrite graincrystal boundaries, to which I ascribe in a large measure the increased impact value of my improved cast ferrous metal alloy, and which arrangement is called herein for short, net-work structure.

In the accompanying drawings forming a part of this speciiicationz- Fig. 1 is a copy of a photomicrograph at 1000 diameters of a polished and etched fracture surface of regular white iron of normal analysis, malleableized in the usual manner;

Fig. 2 is a graph of theheat treatment accorded to white iron in the malleableizing process;

Fig. 3 is a. copy of a photomicrograph at 1000 diameters of a polished and etched fracture surface of regular white cast iron after heat treatment according to the said Jewett and Harris Patent 2,008,452, above noted; said heat treatment comprising heating to about 1600" F. then immediately quenching, then reheating to about 1325 F. and then again quenching; the illustration exhibiting a spheroidized-pearlitic-sorbitic grain structure;

Fig. 4 is a graph of the heat treatment accorded to the metal shown in Fig. 3;

Figs. 5 and 6 are copies of photomicrographs at i 1340 degrees F. for ve hours andquenched. 'I'he said alloy thereafter tested as follows:- tensile strength 90,700 pounds, elastic limit 56,300 pounds, and elongation 13.5 percent. Critical temperatures, as dened herein, are temperatures at which retardation occurs in the heating and coolingcurves of iron-carbon alloys, and are attributed to chemical and physical rearrangement of the iron and carbon. In alloys of this type, it is commonly ,dened as the carbon combining temperature. The critical temperature of my metal alloy may range between- 132 5 F. and

1375 F. l A

Fig. 7 is a graph of the heat treatment accorded to the metal lshown in Figs. 5 and 6, and

Figs. 8 and 9 are copies of photomicrographs at 200 diameters and 1000 diameters respectively,

of an etched arid polished fracture surface of my new alloy, containing 2.27 percent carbon, 0.89 percent silicon, 0.83 percent manganese, and 1.00 percent copper; which alloy has been heated to 1700 degrees F. for thirty hours, then quenched below the critical temperature, then reheated to 1270 degrees F. for thirty hours, then heated to 1340 degrees F. for two and one-half hoursA and thereafter quenched. After such treatment the said alloy tested as followsz--tensile strength 80,000 pounds, elastic li1 r1it 55,800 pounds, and elongation 17.0 percent.

Fig. 10 is a sketch constituting a diagrammatic representation of the structure shown in Fig. 3./ It is representative of the structure of the final product obtained in accordance with theprocess disclosed in the aforesaid Jewett et al. patent. Fig. 11 is a similar diagrammatic representation of the structure shown in Fig. 9, representing the microstructure of the final product produced in accordance with the present invention. In Figs. 10 and 11 the various constituents have been identified in the drawings.

, One method of making my alloy of white iron, copper and manganese, is to pour molten iron having a composition corresponding to regular white iron into a. ladle containing f erromanganese in suicient amount to bring the manganese content of the resulting alloy as high as 0.65 to 1.10 percent. The ladle will alsoA contain copper in small pieces, such as stampings from .thin sheets, in an amount sufficient/to make the copper content of the alloy between, say 0.50l

to 1.50. percent. The resulting White iron,- copper,-mangar i'ese alloy, when made in \this manner, will, when cast, have a composition substantially within the following limits- Percent Carbon 1.90 to 3.00 .Siliconav `1 1.30 to 0.60 Manganese..V 0.65 to 1.10 Copper L 0.50 to 1.50 Phosphorus A 0.08 to 0.16 Sulphur c; f 0.05 t0 0.12

After being subjected to the heat-treatment hereinafter described, this new alloy will be a cast iron product having physical characteristics within the following limits- Tensile strength Impact va1ue foct pounds--- 3oto 15 pounds per sq. in' 67,500 to 110,000 Elastic limit v f pounds per sq. in-- 47,500 to 65,000 Elongation in 2'' percent 18 to 12 Hardness (Brinell) to 220 The average corrosion resistance of my new cast iron product, that is to say the rate of loss of metal in milligrams per square centimeter of l exposed surface when tested with the same solutions, for the same length of time and under the same conditions as the malleable iron mentioned hereinbefore, is as followssalt water solution 0.016

5% sulphuric acid solution v 2.352 25% tannic acid solution 0.047 5% lactic acid solution. 0.075 5% hydrochloric acid solution 0.511

From a'comparison of these physical property tables, it is to be clearly seen that my new cast- Iferrous alloy has good ductility, a greater average placed in a suitable furnacehaving a reducing atmospherethat is to say.one which will not remove carbon from the surface of the castingand brought to a temperature above the critical,

process, graph'i-y that isto say, from about 1600 degrees F. to about 1800 degrees F. This temperature rise may be at a gradual rate and in the example shown in Fig. 7 covers a period of fifteen hours. 'I'he alloy is then held at the predetermined temperature, say 1725 degrees F., for a suiiicient time to entirely decompose the massive cementite particles, the .carbon migrating and forming nely divided graphite nodules; and after this step of the process is completed the matrix is in the austenitic form. The time required for decomposing the cementite and forming austenite is variable with the section and quantitative analysis A of the alloy but will usually run between tenhours and thirty-five hours, after which time the alloy is removed from the furnace and quenched in any suitable medium such asair, water, or oil, and brought to a temperature well below the critical, for example, to a temperature of'about 1200'degrees. i "J After the temperature has'been lowered below the critical, the alloy is placed in a suitable furnace which has previously been heated to between say 1250 degrees F. and 1300 degrees F., andl preferably toA approximately 1270 degrees F. (somewhat below the critical range) and held therefor a suicient time to allow the cementite, which is now in pearlitic form, to'become completely spheroidized and uniformly distributed throughout the entire matrix in minute particles.

4The break-down of the pear-lite into ferrite and graphite during this part of the process I. be-

lieve to be largelyzprevented by the action of the.

excess of a retarding 'element such as manganese. The structure of the metal at this stage is shown by the diagrammatic representation of Fig. 10,

and it will `be noted that in this condition the .structure corresponds to that" obtained inf`ac` cordance withthe process of the aforesaid Jewett et al. patent. After a timesuflicient to secure theabove noted rearrangementof the cementite particleswhich time-period will vary with the size and shape. of the articlel being treated, but which usually ranges between ten and thirtyilve hours-fthe temperature'is raised to between 1325 degrees F. and say 1360'degrees F. Within i this last mentioned temperature range, a. rear.

rangement of the spheroidized cementite particles takes place and they appear to migrate and rearrange themselves into a compactly interlocking structure along the ferrite grain-crystal boundaries. This is the structure of the final product of the present invention, and it may be understood `iy reference to the diagrammatic representation of Fig. 11, which clearly shows the concentration .of spheroidiz'ed'lcementite in the form of a network, or interlocking, in the ferritey Agrain boundaries, together with some residual spheroidized cementite throughout the grains, i. e., some sphcroidized cementite which has not yet migrated to the grain boundaries. This higher temperature is held for a sufficient time to 4permit this rearrangement of the globular cementite, which is usually between two and one-half and seven and one-half hours, depending upon the `chemical composition, size and shape of the casting, and the tensile strength, hardness, impact value, and other physical properties desired in the product; after which the article is quenched in air, water, oil, or other medium with sufficient rapidity to retain the structure secured at the higher temperature.

The product now has a` microstructure as shown in Figs. 5 and 6 or Figs. 8 rmd 9 wherein the spheroids of cementite, instead of being distributed uniformly throughout the matrix, are

collected and interlocked into the grain boundaries of the original ferrite grain-crystals in such manner as to form a network interlocking the grain-crystals and to greatly strengthen the grain-crystal boundary cleavage planes. I believe Athat the copper contained in my alloy, which is `an accelerator, plays a very important part in securing this networkstructure during the final higher heat treatment, as I have discovered that it requires at least .50 percent copper in the mixture to secure the microstructure shown in Figs. 5 and 6 or Figs. 8 and 9. It is my theory that during the final high temperature, the copper, (which is an accelerant), when it is in excess of .50 percent, tends to neutralize the effect theV -manganese (a retardant), mayI have on the carbon and permits the carbon-iron spheroidized cementite to be expelled from the ferrite grains into an interlocked, closely Woven, network structure along the ferrite grain-crystal boundaries.

When normal White cast iron having no excess manganese and no copper incorporated therein, is

-given the heat treatment shown in Fig. 7, the

microstructure remains substantially the same as shown in Fig. 1, and its physical properties do not differ materially from those lof malleable iron produced from normal white iron and subjected to the malleableizing process.

If white cast iron having manganese in excess of the normal practice of less than .60%, that is to say, white iron having at least .70% manganese; and having no copper, is accorded the heat treatment shown in Fig. 7, its microstructure will besubstantially the same as shown in Fig. 3. After the heat treatment, this product will have a major portion of the carbon divided out of the mixture as fine particles of graphite; however, because of the manganese being above normal, some of the carbon will be retained in carbon-iron combination (FesC) andappears in the microstructure as globular or spheroidized cementite quite uniformly interspersed with no definite arrangement throughout the matrix. The tensile strength and hardness of this high-manganese iron product is greater than that of malleable iron of regular white iron composition; but its impact value is much lower and may be as low as 3 foot pounds. I ascribe this low impact value to the fact that the uniform distribution of the spheroidized cementite throughout the matrix tends toward a rigid and less mobile grain structure, with the result that the fracture takes place through the weaker planes along the ferrite crystal grain boundaries. The character of*the fracture is somewhat influenced by the rapidity of testing. Microscopic examination of fractured pieces of such alloy indicates that when tested slowly in a tensile test, some parts of the fracture are through the ferrite crystal, which type of fracture generally shows good ductility, and elongation may be as high as 15%. A microscopic study of pieces fractured by impact determines that impact fracture is almost wholly along the ferrite grain boundary planes. A fracture of this character quite generally indicates a low impact value.

Photomicrographs of numerous pieces of my new white iron-copper manganese alloy, after being accorded heat treatment as indicated in Fig. 7, that is to say with a quick temperature rise near the end of the heat treatment, show a structure substantially the same as Figs. 5 and 6 or Figs. 8 and 9 in which a major'portion of the spheroidized cementite is closely interlocked as a network Within the grain crystal boundaries of the ferrite; and the physical properties of the several pieces will vary substantially in direct ratio to the time they were held at the final higher temperature. As to the Way the physical propertics may be changed by varying the time at which my cast iron alloy is held at the nal high temperature of my heat treatment, the following figures are given, which I have taken from data compiled from numerous tests, attention being especially called to the change in impact value2- Hours at 1340" F 0 111. 2% 5 7l- Impact value (it, lbs.)- l5 17 2l 24 27 Elongaton 13% 14% 16% 16% 19% Tensile Strength 8l, 200 80 300 82, 200 84. 100 82,000 Elastic limit 57, 57, 100 58, 000 57, 800 58, 100

A microscopic examination of fractured pieces of my heat treated white iron-copper-manganese .alloy which havebeen tested slowly in a testing machine for tensile strengthfindicates that the fracture takes place through the ductile ferrite grain crystals, -but as these crystals are surrounded by a network of interlocking spheroids of cementite, which are harder and tougher than the ferrite crystals, the fracture must also pull apart. the interlocking spheroids, which, I believe, ac-

ture is always indicative of high impact value as it takes considerable force under impact to tear apart the ferrite 'grain crystals.

If the product is placed in a vise and struck a sharp quick blow with a hammer, it shows a very tough fracture and will withstand considerable impact force before yielding, very much more so than a malleable iron product or other heat treated cast iron product.

After effecting the heat treatment described, my alloy will have p sical and corrosion-resistant properties substantially within the range stated herein, and for a. cast iron product, an exceptionally high impact value. I ascribe the same mentite within the ferrite grain-crystal boundaries, which I believe is attained by my heat treatment of a cast iron alloy having an excess retarder element and an appreciable amount of an accelerator element.

While I have described my invention by reference 4to certain practical embodiments in order that the same may be used by those skilled in the art, it will be obvious that other embodiments may be'made without departing from the principles of the invention, and, accordingly, it will be understood that the scope of my invention is not to be limited except as may be required by the following claims.

I claim- 1. As a new article of manufacture, heat treated white cast iron alloy containing copper from about 0.5 to 1.5 per cent, manganese from about 0.6 to 1.1 per cent, and characterized by containing spheroidized cementitea substantial proportion of which is interlocked in a network structure along the ferrite grain boundaries.

2. As'a new'article of manufacture, spheroidzed White cast iron alloy containing from about 0.65 toabout 1.1 per cent of manganese, from about 0.5 toaabout 1.5 per cent of copper, having spheroidized cementite interlocked in a network along the ferrite grain boundaries, and having a tensile strength of from about 67,500 to about 110,000 pounds per square inch, an elastic limit of from about 47,500 to about 65,000p'ourids per square inch, and an impact strength of at least about 15 foot pounds.

3. That method of producing heat treated white cast iron products; comprising heat treating white cast iron containing copper in excess of 0.5'per cent, and manganese in excess of 0.6 percent, said treatment comprising heating the alloy at temperatures above and below the critical range for times sufficient to produce therein substantially uniformly distributedl spheroidized cementite; and further heat treating said iron at a temperature within the critical range of the alloy for a time suicient to cause saidlspheroidized cementite in the presence of said copper to migrate to and from an interlocked network structure along the ferrite grain boundaries.

4. That method of producing .heat treated F. for' a time to hours;l and then quenching.

white cast iron products, comprising heat treating white cast iron containing copper from about 0.5 to 1.5 per cent, and manganese from about 0.6 to 1.1 per cent, said heat treatment comprising heating the' alloy at from about 1600* to 1800 F. for a time suiiicient to decompose massive cementite, quenching to below the critical temperature, reheating to from about1250 to 1300 form spheroidized cementite: then raising the temperature to 1325 to 1360 F. for a time'suftlcient to cause said spheroidized cementite to migrate to and form an interlocked network structure along the ferrite grain boundaries.

5. A method of making heat treated white cast iron according to claim 3, the white cast iron alloy containing from about 0.5 to 1.5 per cent of copper, and about 0.6 to 1.1-per cent of manganese.

6. That method of heat treating white cast iron alloys comprising subjecting a white cast iron.

alloy containing from about 0.5 to 1.5 per cent of copper,and about 0.6 to 1.1 per cent of manganese.v to a temperature above the critical ternperature for a time sucient to decompose massive cementite and deposit graphitic carbon;

i quenching to below the critical temperature;

raising the temperature to a point adjacent but below the critical temperature, and'maintaining it thereat for a time suiicient to spheroidize cementite substantially uniformly throughout the matrix; then raising the temperature to, and maintaining it within, the critical range, and thereby causing a substantial amount of spheroidized cementite to migrate and interlock in a network structure along the ferrite grain boundaries; and cooling the alloy to 7 The method of heat treating white cast iron alloys containing from about 0.5 to 1.5 per cent of copper, and about 0.6 to 1.1 per cent of manganese', which comprises heating said alloys to from about 1600` F. to about 1800 F. for a period of time to decompose massive cementite; then quenching to below the critical temperature; reheating to a temperature of from about 1250 F. to about'1300 F. for a period to spheroidize the cementite; then heating in the critical range,

from 1325 F. to labout 1360 F., for several A J. SPARLNG.

preserve said structure.v

dii 

